On the Reverse of Streamwise Velocity Deficit in Formation of Boundary-layer Streaks

다국어 초록 (Multilingual Abstract)

The phenomenon of transformation of streamwise velocity deficit to excess in a near-wall wake behind a flat-plate roughness observed previously in numerous experiments is analyzed qualitatively by means of theories of optimal disturbances based on linearized Navier-Stokes and linearized boundary layer equations. It is shown that the reverse of the velocity deficit can accompany the excitation of a streak and that the formation of two maxima in the disturbance stream wise velocity profiles also observed in the experiments can be a side effect of the streak nonoptimality. An experimental approach aimed to provide quantitative data for comparison with a numerical solution of corresponding initial value problem is suggested.